With its exquisite sensitivities to sound, to tilt, to linear motion, to rotational motion, and to vibration, the inner ear serves as a crucial element in orientation, posture, eye and head movement, and communication. Within each of these sensory modes there are important subdivisions. For example, while some sensory channels from the ear signal actual levels of tilt, motion, sound intensity or vibration, others signal only changes in those levels. Presently, even the divisions of the major sensory functions among the organs of the ear are debated, and subdivisions of those functions within individual organs remains generally in the realm of pure speculation. Furthermore, important morphological details of inner-ear structural specializations that might correspond to these functional specializations remain unresolved. The purpose of this research project is twofold. First, with newly developed methods, structural details of the inner ear will be examined and clarified. Second, with newly developed methods involving injection of fluorescent dye into single nerve fibers whose functions have been identified electrophysiologically, the major divisions and subdivisions of function within the ear will be identified conclusively. With structure-function correspondence thus identified, more definitive theories of inner-ear mechanism will be possible.